Active site conformation in myoglobin as determined by X-ray absorption spectroscopy

Area of Science:

• Biophysics
• Structural Biology
• Spectroscopy

Background:

• Myoglobin (Mb) is a crucial protein for oxygen transport and storage.
• Understanding the active site's structure and dynamics is key to its function.
• X-ray absorption fine structure (XAFS) spectroscopy is a powerful tool for atomic-level structural analysis.

Purpose of the Study:

• To investigate the structural and dynamic properties of myoglobin's active site.
• To analyze thermal and static disorder using the XAFS Debye-Waller factor.
• To compare the temperature-dependent behavior of different myoglobin forms.

Main Methods:

• X-ray absorption fine structure (XAFS) experiments were conducted on various myoglobin (Mb) forms.
• Debye-Waller factor analysis was used to quantify disorder as a function of temperature.
• Structural data were compared with existing X-ray crystallography findings.

Main Results:

• Structures of deoxyMb, MbCO, and MbO2 were consistent with prior crystallographic and XAFS data.
• Ferrous MbNO active site revealed 5 nitrogens at 2.02 Å and a short 1.76 Å NO bond.
• The XAFS Debye-Waller factor's temperature dependence for Mb proteins (except deoxyMb) fit the Einstein model.
• DeoxyMb exhibited a large low-temperature disorder, deviating from the Einstein model.

Conclusions:

• Myoglobin's active site structure is well-defined across different ligand-bound states.
• Deoxy-myoglobin displays unique temperature-dependent dynamics, suggesting conformational substates.
• XAFS spectroscopy effectively probes dynamic disorder and conformational flexibility in proteins.